Here is a sample solution of export PNG:

function exportPNG(pth){
  var str = "";
  for (var i=0;i<pth.length;i++) str += u16to8(pth.charCodeAt(i));
  var act = "/version 3"
  + "/name [ 4 73657431]"
  + "/isOpen 1/actionCount 1"
  + "/action-1 {/name [ 7 616374696f6e31]"
  + "/keyIndex 0/colorIndex 0/isOpen 1/eventCount 1"
  + "/event-1 {"
  + "/useRulersIn1stQuadrant 0"
  + "/internalName (adobe_exportDocument)"
  + "/isOpen 0/isOn 1/hasDialog 1/showDialog 0"
  + "/parameterCount 6"
  + "/parameter-1 {/key 1851878757/showInPalette 4294967295"
  + "/type (ustring)"
  + "/value [ " + str.length/2 + " " + str + "]}"//Fullpath of the target file in UTF-8 Hexadecimal
  + "/parameter-2 {/key 1718775156/showInPalette 4294967295"
  + "/type (ustring)"
  + "/value [ 16 41646f626520504e4720466f726d6174]}"
  + "/parameter-3 {/key 1702392942/showInPalette 4294967295"
  + "/type (ustring)/value [ 3 706e67]}"
  + "/parameter-4 {/key 1936548194/showInPalette 4294967295/type (boolean)/value 0}"
  + "/parameter-5 {/key 1935764588"
  + "/showInPalette 4294967295/type (boolean)/value 1}"
  + "/parameter-6 {/key 1936875886/showInPalette 4294967295/type (ustring)/value [ 0]}}}"

  var tmp = File(Folder.desktop + "/tmpSet1.aia");  
  tmp.open('w');  
  tmp.write(act); 
  tmp.close();
  app.loadAction(tmp); 
  app.doScript("action1", "set1", false);  
  app.unloadAction("set1","");
  tmp.remove();
  }


function u16to8(cd) {
  var out =
  (cd < 0x80
  ? toHex2(cd)
  : (cd < 0x800
  ? toHex2(cd >> 6 & 0x1f | 0xc0)
  : toHex2(cd >> 12 | 0xe0) +
  toHex2(cd >> 6 & 0x3f | 0x80)
  ) + toHex2(cd & 0x3f | 0x80)
  );
  return out;
  }


function toHex2(num) {
  var out = '0' + num.toString(16);
  return out.slice(-2);
}


var pth = Folder.selectDialog("target Folder?").fsName + "/test.png";
exportPNG(pth);

We have to write string codes of File and Folder names in UTF-8.

Here is one of the workarounds: the usage of actions in CS6+.

It's not ideal, but it does work. There's the issue of this action only saving the active document under its name in a folder - I do not know how to set a complete file path - but basically you take a recorded save jpg action, paste it and replace the hex-encoded lines in it to put in your own folder path. Then load the action and play it, and then remove it if you so wish.

Or you can just simply have this action not dynamically constructed like this, but always in your palette, and you treat the destination folder as a "hot folder" and make your script grab files from it after they are done being written (may need a sleep loop to wait until file is complete?).

Here's a dynamic-like example, since I'll probably come back to this place to read this again many times

#target illustrator
function test(){


  String.prototype.hexEncode = function(){
  //http://stackoverflow.com/questions/21647928/javascript-unicode-string-to-hex
    var hex = '';
    for(var i=0;i<this.length;i++) {
        hex += ''+this.charCodeAt(i).toString(16);
    }
    return hex;
  };


  function writeFile(fileDestStr, contents){
  var newFile = File(fileDestStr);
  newFile.open('w');
  newFile.write(contents);
  newFile.close();
  };


  var actionStr = [
  "/version 3",
  "/name [ 4",
  " 54657374",
  "]",
  "/isOpen 1",
  "/actionCount 1",
  "/action-1 {",
  " /name [ 12",
  " 53617665204d79204a504547",
  " ]",
  " /keyIndex 0",
  " /colorIndex 0",
  " /isOpen 1",
  " /eventCount 1",
  " /event-1 {",
  " /useRulersIn1stQuadrant 0",
  " /internalName (adobe_exportDocument)",
  " /localizedName [ 6",
  " 4578706f7274",
  " ]",
  " /isOpen 0",
  " /isOn 1",
  " /hasDialog 1",
  " /showDialog 0",
  " /parameterCount 7",
  " /parameter-1 {",
  " /key 1885434477",
  " /showInPalette 0",
  " /type (raw)",
  " /value < 104",
  " 0a00000001000000030000000200000000002c0102000000000000000100000069006d006100670065006d00610070000000310000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001000000",
  // What is the world is this? ^^^ ',imagemap' followed by the remnants of the active file's name? It makes not a lot of sense, anyone know?
  " >",
  " /size 104",
  " }",
  " /parameter-2 {",
  " /key 1851878757",
  " /showInPalette -1",
  " /type (ustring)",
  " /value [ PUT_FOLDERPATH_CHAR_LENGTH_HERE",
  " PUT_HEX_FOLDERPATH_HERE",
  " ]",
  " }",
  " /parameter-3 {",
  " /key 1718775156",
  " /showInPalette -1",
  " /type (ustring)",
  " /value [ 16",
  " 4a5045472066696c6520666f726d6174",
  " ]",
  " }",
  " /parameter-4 {",
  " /key 1702392942",
  " /showInPalette -1",
  " /type (ustring)",
  " /value [ 12",
  " 6a70672c6a70652c6a706567",
  " ]",
  " }",
  " /parameter-5 {",
  " /key 1936548194",
  " /showInPalette -1",
  " /type (boolean)",
  " /value 0",
  " }",
  " /parameter-6 {",
  " /key 1935764588",
  " /showInPalette -1",
  " /type (boolean)",
  " /value 1",
  " }",
  " /parameter-7 {",
  " /key 1936875886",
  " /showInPalette -1",
  " /type (ustring)",
  " /value [ 1",
  " 31",
  " ]",
  " }",
  " }",
  "}"
  ].join("\n");


  if(app.documents.length == 0){
  return;
  }


  var dest = Folder.selectDialog("Pick a folder and save the 300ppi CMYK JPEG there.");
  if(!dest){
  alert("Cancelled");
  return;
  }


  var destStr = decodeURI(dest.fsName);
  var actionFileDestStr = Folder.desktop + "/MyAction.aia";
  writeFile(actionFileDestStr, actionStr.replace("PUT_FOLDERPATH_CHAR_LENGTH_HERE", destStr.length).replace("PUT_HEX_FOLDERPATH_HERE", destStr.hexEncode()));
  var actionFile = File(actionFileDestStr);
  app.loadAction(actionFile);
  app.doScript("Save My JPEG", "Test");


  //clean up
  actionFile.remove();
  app.unloadAction("Test", ''); // thanks qwertyfly!


};
test();

Class

ExportOptionsJPEG

Options which may be supplied when exporting a document as a JPEG file.

Class

Sorry but not possible with scripting except with a lot of workarounds. The other thing that might mess everything up is most software expects JPG files to be RGB and 72 ppi. Adobe can read CMYK/300 ppi JPG files but with other software you might get garbage.